A wide variety of hydrocarbon conversion processes encountered in the petroleum refining industry are catalytic in nature and many of them use zeolite catalysts, for example, cracking, as described in U.S. Pat. Nos. 3,700,585 and 3,907,663; hydrocracking as described in U.S. Pat. No. 3,923,641; dewaxing and hydrodewaxing as described in U.S. Pat. Nos. Re. 28,398, 3,700,585, 3,956,102, 4,110,056 and 3,755,138; aromatization processes of the kind described in U.S. Pat. Nos. 3,806,443, 3,767,568, 3,753,891, 3,770,614 and 3,843,740 and alkylation as described in U.S. Pat. No. 3,641,777. They have also been used or proposed for use in a number of petrochemical processes, for example, in alkylation processes of the kind described in U.S. Pat. Nos. 3,668,264, 3,251,897, 4,117,024, 4,049,738 and 4,086,287, isomerization processes of the kind described in U.S. Pat. Nos. 4,100,214 and 4,101,596 and disproportionation processes as described, for example, in U.S. Pat. Nos. 4,106,788 and 3,856,871. Their use in the production of hydrocarbons from other materials such as synthesis gas, methanol, dimethyl ether (DME) or other oxygenated materials is described, for example, in U.S. Pat. Nos. 3,894,102 to 3,894,107, 3,899,544, 4,039,600, 4,048,250 and 4,035,430. In these processes various kinds of zeolites may be used either alone or in combination with one another or with other catalytic materials. Zeolites may be characterized as being small pore materials such as erionite or zeolite A; large pore materials such as zeolite X, zeolite Y or mordenite and the so-called intermediate pore size zeolites exemplified by the ZSM-5 family including ZSM-5 itself, ZSM-11, ZSM-12, ZSM-23, ZSM-35 and ZSM-38.
In some of these processes, the catalyst contains two different types of zeolite. For example, the cracking processes described in U.S. Pat. Nos. 3,578,403, 3,849,291, 3,894,931 and 3,894,934 may employ catalysts which include an intermediate pore size zeolite such as ZSM-5 together with another zeolite, for example, a synthetic faujasite such as zeolite X or zeolite Y.
In many of these processes, the catalyst is required to have a high physical strength in order to resist the stresses which it encounters in use. The catalyst should have good crushing resistance, abrasion resistance and attrition resistance, particularly in processes such as fluid catalytic cracking (FCC) where the catalyst is maintained in a constant state of movement. In order to confer the desired strength, the zeolite is usually incorporated into a binder or a matrix such as a clay, silica, or a metal oxide such as alumina. After the zeolite has been composited with the binder or the matrix, the mixture is usually sintered at a high temperature. Sintered clay matrices confer good physical strength but have the disadvantage that the high sintering temperatures which are necessary tend to destroy the activity and crystallinity and crystallinity of the zeolite. It would therefore be desirable to find some way of preserving the activity and crystallinity of the zeolite while, at the same time, retaining the strength characteristics of the sintered clay composites.
An associated problem which is encountered with the catalyst combinations such as the ZSM-5/faujasite combinations mentioned above is that the combination may require treatment in order to confer a desirable attribute on one of the zeolites but at the same time, this treatment may adversely affect the other zeolite. For example, the ZSM-5/faujasite cracking catalysts need preliminary steaming in order to reduce the cracking activity of the faujasite; the steaming, however, tends to deactivate the ZSM-5 so that it no longer performs its required function of improving product octane number as well. It would therefore, in this case, be desirable to find a way of stabilizing the zeolite so that it may withstand the treatments which it will undergo.